The invention relates to a method for limiting the force action of a robot part, such as a robot arm, on an external object during a collision.
If during working robots collide with external objects there can be considerable damage both to the object and to the robot. Thus, as a rule in the possible work area of a robot there should be no external objects, either in the form of material articles or persons. In order to protect the person or robot a protection is provided by fences or the like in defined work cells and these are secured in such a way that on entering the work cells, e.g. due to the opening of a door or the crossing of monitored lines, the robot is immediately stopped. It can optionally only be moved manually at a reduced speed. The stopping of the robot can give rise to considerable disadvantages, which may be of a business efficiency nature (downtime) or of an operational nature, such as damage to workpieces on which working was taking place at the time of the stoppage and which are consequently undesirable.
Miniature robots are known, in which kinetic energies and therefore in the case of a collision the forces which act are greatly reduced, but during a sequence of operations of a robot can be in areas leading to damage to material articles or persons, as well as to the robot. As a result of the aforementioned disadvantageous effects of an immediate stoppage of the robot when objects enter its work area, an attempt is made to avoid a stopping of the robot solely as a result of the fact that an object enters its work area. It is also necessary for a robot to approach objects, such as workpieces, in order to e.g. grip, machine or otherwise deal with the same. Here again collisions can occur, i.e. an approach with undesirably high speeds, kinetic energies and therefore undesired, high force actions.
In connection with such miniature robots it has been proposed that in the case of a collision a stoppage is brought about by the acting force with the exceeding of a predetermined inertia moment and therefore the drive motor current. It has already been proposed for reducing the force action to provide the robot or its parts with elastic or viscoelastic coverings or casings. In the first-mentioned case it has been considered disadvantageous that as a result the robot stoppage caused by the motor current is unacceptably delayed in the case of a collision and is to be prevented by a viscoelastic covering, i.e. the response times are to be shortened compared with a purely elastic covering (EP 689 903 A1). However, in all cases the force action is too high if the robot is to operate at optimum speeds for the particular operating process. However, the robot efficiency is reduced if from the outset the speeds are generally and fundamentally reduced for the entire sequence of operations in such a way that in the case of a collision, optionally taking account of the cushioning coverings, damage is reliably avoided.
The problem of the invention is therefore to provide a method for limiting the force action of a robot part in the case of a collision and which allows an optimization of the sequence of operations of the robot, whilst avoiding the aforementioned disadvantages and taking account of safety requirements.
According to the invention the set problem is solved with a method of the aforementioned type, wherein as a result of the maximum allowed force acting on the object in the case of a collision, maximum force Fmax, a corresponding maximum permitted kinetic energy, maximum energy E/kin,max of the robot part is determined wherein continuously at adequately short time intervals the actual kinetic energy, actual energy Ekin, of the robot part is determined and wherein on exceeding the maximum permitting energy Ekin,max, the actual operating speed v of the robot is reduced.
The kinetic energy can be reduced as a function of the situation or by a preset value. It can be an absolute or a relative value and in the latter case relative to the instantaneous operating speed, or an optimum operating speed resulting from the operating process. The reduction is generally in a range between 3 and 10% and is preferably 5%.
According to a preferred development, with which the efficiency of the robot subject to the method of the invention is increased or optimized, on exceeding the actual kinetic energy Ekin compared with the maximum permitted kinetic energy Ekin,max a check is made to establish whether the actual instantaneous operating speed is below the speed appropriate for the operating process performed by the robot and then the actual operating speed is increased in absolute or relative terms by a predetermined value.
In order to increase the maximum kinetic energy and therefore the efficiency for a given maximum force action, according to a further development of the invention in the case of the predetermined maximum permitted force Fmax, the permitted maximum kinetic energy Ekin,max is increased by a cushioning covering on robot parts and an elastic or viscoelastic covering or casing can be provided.